Prior to the advent of digital medical imaging, images were film-based and would be attached or “hung” on vertical light-boxes for review by clinicians such as radiologists. Typically, support staff would prepare the case for reading, hanging the images according to a chosen hanging protocol. The hanging protocol would define the relative hanging positions of the images according to criteria such as date/time of acquisition, orientation of acquisition, anatomy, type of study, preference of the reading clinician.
Modern medical imaging devices such as CT scanners or MRI scanners can provide a variety of different views of a region of interest. Increasingly, medical images are reviewed in digital format on high-resolution computer monitors. One method of review is using viewing software supplied with a Picture Archiving and Communications System (PACS) or associated with scanner devices. This software divides the display into a number of views, for example rectangular areas each of which displays an image or associated information. Such views can comprise, for example, views in different planes such as coronal, sagittal and axial planes and/or different types of views such as 2D sectional views, 3D or pseudo 3D rendered views and the like.
Display of images using software allows for more flexible methods of display, and radiologists have adapted their review methods to take advantage of these new capabilities. A basic example is the ability to scroll through a set of related images within a single view rather than displaying them simultaneously in many separate views. An extension of this is to spatially and/or temporally register multiple sets of images and scroll through them in synchrony. A further extension is to display additional localizer images, for example images acquired orthogonally to the primary images, and display cross-section indicator lines on these, indicating the anatomical location of the primary images.
PACS viewers or similar other viewers offer a wide range of additional capabilities, including contrast adjustment, measurement, panning, zooming, and so on, some of which may optionally be applied to multiple linked views simultaneously. In general, a characteristic of such viewers is that the user interacts with the views using, for example a mouse, a touch screen or a keyboard, and the images in the view, and in related views, change accordingly.
A PACS or other software-based hanging protocol, rather than being a set of encoded preferences/instructions enacted by support staff on receipt of film-based images, may be a software-automated display method either automatically applied based on some matching rules, or selected from a list by a user, when loading digital images. The Digital Imaging and Communications in Medicine (DICOM) standard provides optional guidance for the construction and interpretation of such hanging protocols.
When analysing such imaging data, it is often beneficial to view a region of interest using a variety of concurrently displayed views of the region, e.g. using a multiplanar reconstruction (MPR), or to present a selection of associated views of the same or different regions. For example, this may allow views in different planes or different image types to be presented simultaneously for direct comparison.
The selection of the views for display and the order and relative positioning of the views can be specified by a hanging protocol. The use of hanging protocols ensures that the views are presented to the user in a consistent and repeatable manner and in a way that allows for optimal analysis. For instance, in a simple example a hanging protocol for analyzing for a particular condition associated with a particular body part may specify a 2×2 grid, with a transverse or axial view in the top left hand corner, a view in the coronal plane in the top right hand corner and a sagittal view in the bottom left hand corner.
For more specialist tasks, various forms of advanced visualization may be performed. For example, Multi-Planar Reformatting (MPR) processes the original images produced by a CT, MRI or other three-dimensional scanner to produce cross-sectional images at any other orientation through the patient. Various forms of 3D volume rendering process the original images to provide near-photo-realistic 3D representations of anatomy. Automatic segmentation techniques identify and highlight or hide particular anatomical structures. Many other similar advanced techniques and rendering modes exist.
Advanced visualization techniques greatly expand the type of views and the potential interactions and linkages between them. For example, on loading images of a portion of the vasculature, software may provide MPR views in Axial, Coronal and Sagittal planes, a 3D Shaded Volume View, a Curved Planar Reformatting view derived from a manually or automatically determined vessel centreline, and one or more planar MPR views orthogonal to particular points on the vessel centreline. Changing the contrast in one MPR view may similarly change the contrast on some or all of the other MPRs. Scrolling, panning or zooming one MPR view may cause related changes to other MPRs. Editing a vessel centreline may be performed on one or more views, causing updates to other views. Additionally, some of these views may be judged to be of lower diagnostic importance or relevance than others.
Choosing which views to include, how the views interact, and the relative sizes and positions of views is part of the skill of product design for advanced visualization software. These choices can also be regarded, or offered, as types of hanging protocol.
The main work of a radiologist may be done within a darkened radiology reading room, using one or more specialist high-resolution monitors connected to a computer workstation and/or server. However, other types of users exist, for example surgeons, oncologists, cardiologists, nurses and so on. These users may view medical images on separate specialist systems, designed, for example, for the surgical theatre or for carrying between hospital wards. Alternatively, they may use systems providing easy access to images from a standard desktop or laptop computer, or mobile tablet device, perhaps through software hosted within a web browser. Similarly, radiologists working on call from home may use teleradiology viewers providing image review functions requiring less screen space and network bandwidth. From the above, it can be appreciated that hanging protocols may vary according to individual preference, user role, available hardware, location, context, and so on.
It is common for radiologists and other types of user to collaborate face-to-face while reviewing or discussing images and associated data. For example, it is common practice to discuss treatment decisions in multi-disciplinary team meetings or other, less formal interactions.
In the case of a collaboration between, say, a radiologist and a surgeon, the radiologist may, for example, be using a laptop and the surgeon may have a tablet device. Each of the users must separately look up and load the relevant patient data from some source (local hard disk or over a network via wireless or cable). Each user may have different, role-specific viewing software. They may be unused to each other's viewing software and this may hinder easy interpretation of the case. Each viewing software may behave entirely independently of the other. There is no linkage of navigation, visualization settings and so on.
Because one or both of the radiologist and the surgeon are away from their typical viewing environment (which may include multiple specialised displays) their standard hanging protocol may be unsuited to the display they have brought with them to the collaboration. For example, there may be insufficient space for both the essential views and the less essential ones. The shape and resolution of the display may fail to match the requirements of the standard hanging protocol (e.g. convenient full size display of two 512×512 pixel images)
FIG. 1 shows an implementation of a hanging protocol in a multiplanar reconstruction (MPR) image display system 5. This image display system 5 comprises a workstation 10 having a processing unit 15 and an associated display unit 20. The display unit 20 comprises, for example, a high resolution 10 Mpixel display. Upon initiating a work session, the purpose of the session is established, e.g. the modality used and the procedure that it is being used in connection with. The relevant properties of the attached display unit 20, such as the resolution and size of the display are also established.
Each hanging protocol may have an associated set of rules that set out the circumstances in which the hanging protocol is applicable, for example the purposes and display properties it can be used for. In this way, a hanging protocol appropriate for the session can then be selected. The processing unit 15 then configures the display unit 20 to display the required images in the relative positions specified in the hanging protocol.
Each of the views should be displayed with an acceptable resolution and size in order to allow the user to identify and assess the relevant image features. In order to provide acceptable views, many image display systems use very high resolution display technology, such as 10 Mpixel monitors. It will be appreciated that the high resolution display units 20 favoured in systems such as that of FIG. 1 can be expensive and such systems tend to be bulky, heavy and lack portability.
Devices such as workstations, tablet computers, smartphones and the like are becoming increasingly common in hospitals. However, the display units used by these devices are generally of significantly lower resolution than the high resolution displays used by medical image display systems such as that of FIG. 1. For example, the screen of an Apple® iPhone® 4s is 906 pixels by 640 pixels at a resolution of 326 pixels per inch, whilst an Apple® iPad® 2 has a 1024 pixel by 768 pixel screen at a resolution of 132 pixels per inch. It will be appreciated that these specifications are significantly below the specifications of displays commonly found in modern specialist medical image display systems.
Despite advances in monitor technology, alternative ways of displaying of medical imaging data may be desirable.